Sucrose Metabolism in Ripening Muskmelon Fruit as Affected by Leaf Area

Abstract

<jats:p>Muskmelon <jats:italic>(Cucumis melo</jats:italic> L.) fruit lack a stored starch reserve and therefore depend on translocated photoassimilate from the leaf canopy for sugar accumulation during ripening. The influence of canopy photosynthesis on sucrose' accumulation within muskmelon fruit mesocarp was examined. Canopy photosynthetic activities were estimated in a sweet and a nonsweet genotype. Photosynthetic rate of the nonsweet genotype, on a per-plant basis, was only 56% of that of the sweet genotype. The effect of limiting leaf area of the sweet genotype on carbohydrate concentrations and sucrose metabolizing enzymes within the fruit was evaluated. A 50% reduction of leaf area 8 days before initiation of fruit sucrose accumulation resulted in canopy photosynthesis similar to that of the nonsweet genotype. Reduced photosynthetic activity resulted in slightly lower soluble-carbohydrate concentration in the fruit; however, fruit sucrose concentration was three times higher than that reported previously for the nonsweet genotype. The extent to which `fruit sucrose phosphate synthase (SPS) activity increased during maturation was diminished by leaf removal. Acid invertase activity declined in all fruit in a similar manner irrespective of defoliation. A reduction of leaf area of a sweet genotype reduced sucrose accumulation within the fruit. Lower fruit sucrose concentration was associated with lower concentration of raffinose saccharides and lower SPS activity within the fruit. Additionally, insufficient assimilate supply was judged not to be the factor responsible for low sucrose accumulation in a nonsweet genotype.</jats:p>

The changes in physical, bio-chemical, physiological characteristics and enzyme activities of mango cv. Jinhwang during fruit growth and development

“…Fructose and sucrose contents increased until maturity, while glucose content increased at 80 DAA and later decreased at maturity stage. Sucrose accumulation occurred later in fruit development and final sucrose concentration was a high achieved at maturity [28]. Fructose seems to be more effective than sucrose and glucose in promoting fruit set [29] and it is the predominant sugar in mango [25].…”

Impact of secondary-lateral branch removal during watermelon production

“…Leaves close to the fruit bearing node are the most important source of assimilates for cucumber fruit (Murakami et al, 1982) and watermelon fruit (Lee et al, 2005). Alteration in source availability from early growth stages may result in change in the number of fruit set and biomass per fruit, with no change in the sugar content (Hubbard et al, 1990). However, Hubbard and his colleagues reported that when 50% of plant leaves were removed 28 days before harvest, a significant reduction in the soluble solid content of fruit was observed.…”

Leaf:fruit ratio and irrigation supply affect seasonal changes in minerals, organic acids and sugars of mango fruit

“…14 For peach trees, it has been reported that a low leaf:fruit ratio reduces fruit size and sweetness, and delays fruit maturity, as indicated by a late rise of ethylene production. 15 It has also been found that the poorest eating quality of fruit at harvest, induced by low leaf:fruit ratios, was due to lower sucrose and hexose sugar contents in muskmelon 16 and to lower sucrose and higher citric acid contents in peach. 15,17 However, under the same assimilate supply conditions, apple fruit exhibited both the lowest potassium and the highest calcium concentrations, 18 which positively affected fruit storage and reduced disorders.…”